If the old Watergate expression is “It’s not the crime; it’s the coverup,” then today’s equivalent might be “It’s not the crime; it’s the crime’s offspring.”

Federal prosecutors in the Southern District of New York served a sweeping subpoena on President Trump’s inaugural committee on Monday. Nothing could more clearly illustrate the breadth of the president’s legal exposure and the limits of his nearly two-year strategy to attack and undermine special counsel Robert S. Mueller III — because the special counsel’s work is merely the sturdy root of a veritable Mueller family tree. What began as an FBI counterintelligence investigation into Russian interference in the 2016 presidential election has sprouted into multiple investigations in multiple jurisdictions examining multiple possible crimes. The case against the president’s personal lawyer and fixer Michael Cohen is the direct line, the first child. The investigation of the inaugural committee, which sprang from the Cohen case, is the grandchild. And on it goes.

The president no longer faces jeopardy from just one federal criminal probe, but at least three, and not just one prosecutor’s office, but the full resources of the entire Justice Department. In his State of the Union address on Tuesday, Trump asserted that “ridiculous partisan investigations” threatened the “economic miracle” that was happening on his watch. The threat of the investigations, however you characterize them, is to the president himself.

Prosecutors looking into illegality in one area of the president’s life have discovered evidence of potential crimes in other areas. Mueller’s discovery of wrongdoing by Cohen led to a referral to prosecutors in Manhattan, who secured a guilty plea from Cohen for violating campaign finance laws and alleged in court papers that it was Trump who directed Cohen to break the law. That investigation in turn produced evidence of wrongdoing at the Trump inaugural committee, which has led to an investigation of a Trump donor, a Los Angeles venture capitalist with ties to Qatar.

Grand juries have brought down industry titans and a sitting president. So what do we know about the ones working on the Trump-Russia probe? (Gillian Brockell, Danielle Kunitz/The Washington Post)

To open a new investigation, prosecutors need a credible predicate to believe that a crime has been committed. They must develop probable cause to believe they will uncover evidence or the fruit of a crime to persuade a federal judge to issue a search warrant. None of this suggests the witch hunt Trump often claims it is.

Federal investigations are serious business, with high stakes for those involved. Public corruption cases undergo internal scrutiny at the Justice Department to avoid the possibility of political maneuvering. An individual who becomes a target in one wants to limit the possible crimes he faces to as narrow a range as possible. That is doubly true for a political officeholder, who must manage the political fallout of investigations as well as the prospect of being charged in court. Trump, however, is now fighting a legal battle on multiple fronts, both substantively and geographically. He is in jeopardy. Criminal charges once he leaves office or referrals to the House of Representatives for an impeachment inquiry before then are real possibilities.

Compounding all this is the fact that related investigations cross-pollinate. Evidence and cooperating witnesses produced in one case can help prosecutors in another, increasing the risk that wrongdoing, if it exists, will be uncovered. For example, once he pleaded guilty and became a cooperator, the president’s former deputy campaign chairman Rick Gates served as a witness against Trump’s former campaign chairman Paul Manafort at his trial. But as both a former campaign and inaugural staffer, Gates also has information that is useful in the other probes. Mueller recently told a judge in Washington that Gates continues to cooperate in “several ongoing investigations.”

Similarly, Cohen first agreed to plead guilty in the Southern District’s campaign finance probe, but then he became a cooperator for Mueller and provided, in the course of seven interviews, what the special counsel called “useful information’’ concerning certain discrete Russia-related matters core to its investigation. The same is true for Michael Flynn, who has cooperated in at least two separate investigations after pleading guilty to lying to federal investigators about his contacts with former Russian ambassador Sergey Kislyak. The pool of knowledge developed through crossover investigations amplifies prosecutors’ ability to uncover evidence and increases the likelihood they will have sufficient proof to bring charges.

Each new rock the Justice Department turns over holds the potential to launch entirely new lines of inquiry. In addition to the three investigations into the president and the organizations he has headed, Mueller has already referred multiple cases that we know of to prosecutors in Manhattan and Washington. The U.S. attorney in D.C. has secured guilty pleas from a former Senate staffer (for lying to investigators) and a Republican lobbyist (who arranged for foreigners to contribute to the president’s inauguration using straw donors), while SDNY continues to investigate whether prominent lawyers and lobbyists working with Manafort on behalf of Ukraine violated laws on foreign registration. Furthermore, the New York state attorney general is investigating the Trump Foundation, extending the president’s exposure beyond the Justice Department.

If Mueller is indeed winding down in the near future, as acting attorney general Matthew G. Whitaker recently claimed he was, it could only be with referrals to U.S. attorneys’ offices around the country. The reality is that in prosecutions, it’s never over until it’s over. New evidence can come to light at a late stage and trigger new investigations. Mueller’s reported interest in interactions between the representatives of the government of the United Arab Emirates and the Trump transition team seems ripe for such a referral. There are also concerns over potential financial improprieties in the development of Trump Tower Moscow. And this doesn’t even account for any unknown areas Mueller may be pursuing.

It’s this threat of multiple ongoing investigations spanning the foreseeable future that should frighten the president the most. Whatever his personal criminal liability, it’s now proven that the organizations he has run — business, political and governmental — have been populated with actual criminals. Six of his associates, including his longtime friend and political adviser, his lawyer, his campaign chairman, his deputy campaign chairman and a foreign policy adviser have been indicted or pleaded guilty. It would be naive at this point to believe that more such charges are not coming. That apple could fall very near the tree indeed.

Can the president pardon himself? Legal expert Randall D. Eliason answers key questions in the Mueller investigation. (Joy Yi, Kate Woodsome, Danielle Kunitz/The Washington Post)